The present invention is directed to bicycles and, more particularly, to a claw-pole dynamo having a yoke that is formed by plate-shaped members.
Due to configuration and cost considerations, the yoke of a conventional claw-pole dynamo is often formed using pressed sheet metal. However, this type of conventional dynamo has the problem of decreased efficiency due to the generation of eddy current. Accordingly, as disclosed in Japanese Patent Laid-Open No. 2001-37108, a dynamo has a coil fixed to a hub shaft and a casing that can rotate relative to the hub shaft. The casing has a magnet on its inner circumferential surface so that the magnet rotates with the casing. The yoke that houses the dynamo coil comprises multiple laminated thin plate-shaped members to prevent the generation of eddy currents. It is know that in this type of generator, the generation of eddy current decreases in inverse proportion to the square of the plate thickness of the yoke. By forming the yoke using laminated plate-shaped pieces, the thickness can be reduced and the generation of eddy currents can be minimized. However, in the case of a claw-pole dynamo, because the radially outer portions of the yoke extend toward each other in a circumferentially interleaved manner from the axial ends of the dynamo, it is difficult to design an efficient laminated construction. Furthermore, other magnetic members must be placed at the interleaved portion. When such other magnetic members are used, however, magnetic resistance increases and efficiency decreases. Furthermore, such additional magnetic members increase manufacturing costs and the cost of the resulting dynamo.